Jenkins: agents can send HttpResponse-implementing exceptions to the controller, yielding XSS

Impact

The controller accepts exceptions from agents that implement the Stapler HttpResponse interface and lets them shape the HTTP response, so an attacker controlling an agent process can inject script into a controller page. Same practical risk as the other agent-trust flaw in this advisory but a different mechanism and code path: here the vehicle is exception handling in the agent-to-controller channel rather than workspace link generation. On a GPU CI fleet, agents execute untrusted build and training code, so agent compromise is the realistic starting point, and the scope change means the script runs with the controller's origin against an operator's session. Affects Jenkins 2.587 and earlier and LTS 2.580.1 and earlier.

Who can reach it

An attacker in control of an agent process, which then sends a crafted exception over the agent channel. A user must load the affected controller response (UI:R); no prior authentication to the controller is needed by the attacker.

What to do

Upgrade the Jenkins controller past 2.587, or past LTS 2.580.1, per the 2026-10-28 advisory, and restart the controller - the record does not name the fixed version, so confirm it in the advisory. Controller restart with builds drained; agents do not need reimaging unless you believe one was already compromised.

References

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